Rewinding machines are used to produce convolutley wound rolls or “logs” of web material. Rewinders are used to convert large parent rolls of paper into retail sized rolls and bathroom tissue and paper towels. These rewinding machines typically wind a predetermined length of web material about a tubular winding core normally made of cardboard. These rolls or logs are then cut into a plurality of smaller-size rolls intended for commercial sale and consumer use. The tubular winding core section remains inside each convolutley wound roll of web material. In both cases the end product contains a tubular core made of material different from that forming the roll.
Rewinding machines are generally divided into two categories depending on the manner in which the winding movement is provided. The first type of rewinding machine, known as a central spindle rewinding machine (or center winder), a spindle supported on support elements between a pair of side walls receives a tubular winding core on which the roll or log is formed by means of rotation of the spindle which, for this purpose, is associated with drive means. The winding movement is therefore provided centrally by the spindle.
A second type of rewinding machine, known as a surface rewinding machine (or surface winder), the rotational movement of the tubular core on which the roll or log is formed is provided by peripheral members in the form of rollers or rotating cylinders and/or belts with which the roll or log is kept in contact during formation. Exemplary surface winders are disclosed in U.S. Pat. Nos. 3,630,462; 3,791,602; 4,541,583; 4,723,724; 4,828,195; 4,856,752; 4,909,452; 4,962,897; 5,104,155; 5,137,225; 5,226,611; 5,267,703; 5,285,979; 5,312,059; 5,368,252; 5,370,335; 5,402,960; 5,431,357; 5,505,405; 5,538,199; 5,542,622; 5,603,467; 5,769,352; 5,772,149; 6,286,419; 6,565,033; 6,595,458; 6,595,459; 6,648,266; 6,659,387; 6,698,681; 6,715,709; 6,729,572; 6,752,344; 6,752,345; 6,866,220; 7,293,736; 7,909,282; and EPO Patent Application No. 0514226 A1.
The surface winder is comprised of 3 principle winding rolls to perform the surface winding process. These rolls are the upper winding roll (UWR), lower winding roll (LWR), and rider roll (RR). The respective rolls are named due to where or how they contact a winding log. The UWR and LWR contact the winding log on the upper and lower portions respectively and the RR “rides” on the upper portion of the winding log as it increases in diameter as web material is wound thereabout. The winding log enters the surface winder and is adhesively attached to a web material to be wound thereabout in a region of compression disposed between the UWR and LWR. The winding log is initially rotated by the UWR in a region disposed between the UWR and a stationary core cradle and rotationally translates to a region disposed intermediate the rotating, but stationary, UWR and LWR (known as the winding nest region). The RR contacts the surface of the rotating winding log in the winding nest region and translates away from the UWR and LWR as web material continues to be convolutely wound about the winding log.
In an exemplary surface wind system, a web material is convolutely wound about a paperboard core of 1.5″ to 1.7″ diameter and of a length that corresponds to the width of the tissue parent roll which comes from the paper machine, usually in width from 65″ to 155″.
However useful, surface winders do have limitations. For example, the paperboard core that is used as the base for winding the web material is a hollow core and has a low bend modulus and is subject to radial deformation. This is particularly true as the volume of web material wound about the core is decreased. Convolutley wound rolls of web material that are sold in the retail commercial market have a target finally wound roll diameter. The target finally wound roll diameter is selected by manufacturers of such products to provide the appearance of a desirable and saleable product. Additionally, the physical characteristics of the web material wound about the core are constantly changing. These changes are necessitated by the economics for the production of such convolutely wound web material. For example, the material used to produce the underlying web material is a commodity. As the costs of the material increases, market dynamics require that the amount of material used to produce the web material be decreased. In other words, the density, or basis weight, of the web material is constantly decreasing.
Additionally, the web materials are constantly being modified by post formation treatments in the converting processes. Such post formation converting operations include, for example, embossing and calendaring. These post formation web material treatments will typically add thickness (or caliper) to the underlying web material. In order to maintain the appearance imparted to the web material by these converting operations, the winding process must prevent removing these desired characteristics from the winding process by winding the web materials about the cores with low tension. Winding a web material about a core in a low tension environment provides for a ‘loose’ wind. Thus, as the web material is wound about the core, the inherent bend modulus of the winding product disposed within the winding nest is not increased. In other words, the structural stability of the core is not increased in a low-tension winding process as would be observed in a winding process where a web material is wound about a core under high tension as the effective cross-section of the core/web material structure is not appreciably increased.
This drawback to winding a loosely wound web material about a core with a surface winding process typically results in a core/web material system that undergoes structural deformation within the winding nest. An exemplary structural deformation is shown in FIG. 1. Additionally, the core/web material system is often subject to instability within the winding nest that effectively causes the core/web material system to bounce between the UWR, LWR, and RR while disposed in the winding nest. An exemplary and representative bouncing core/web material system is shown in FIGS. 1A and 2.
Thus, there is a clearly defined need to increase the stability and structural strength of the core disposed within the winding nest of a surface winding system. Increasing the stability and structural strength of the core as well as the ensuing core/web material system in situations where the web material has a low basis weight, a high caliper, and processed under low tension can help provide a consumer acceptable convolutley finally wound web material product that meets current manufacturing financial and processing targets.